Low‐cost biosensors that can rapidly and widely monitor plant nutritional levels will be critical for better understanding plant health and improving precision agriculture decision making. In this work, fully printed ion‐selective organic electrochemical transistors (OECTs) that can detect macronutrient concentrations in whole plant sap are described. Potassium, the most concentrated cation in the majority of plants, is selected as the target analyte as it plays a critical role in plant growth and development. The ion sensors demonstrate high current (170 µA dec−1) and voltage (99 mV dec−1) sensitivity, and a low limit of detection (10 × 10−6 m). These OECT biosensors can be used to determine potassium concentration in raw sap and sap‐like aqueous environments demonstrating a log‐linear response within the expected physiological range of cations in plants. The performance of these printed devices enables their use in high‐throughput plant health monitoring in agricultural and ecological applications.

Implantable electrophoretic drug delivery devices have shown promise for applications ranging from treating pathologies such as epilepsy and cancer to regulating plant physiology. Upon applying a voltage, the devices electrophoretically transport charged drug molecules across an ion‐conducting membrane out to the local implanted area. This solvent‐flow‐free “dry” delivery enables controlled drug release with minimal pressure increase at the outlet. However, a major challenge these devices face is limiting drug leakage in their idle state. Here, a method of reducing passive drug leakage through the choice of the drug co‐ion is presented. By switching acetylcholine's associated co‐ion from chloride to carboxylate co‐ions as well as sulfopropyl acrylate‐based polyanions, steady‐state drug leakage rate is reduced up to sevenfold with minimal effect on the active drug delivery rate. Numerical simulations further illustrate the potential of this method and offer guidance for new material systems to suppress passive drug leakage in electrophoretic drug delivery devices.

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In this work, we present a novel method for integrating printed electronic materials with biocompatible cryogels to form stable, implantable hydrogel-based bioelectronic devices that show stable long-term operation inside plant tissue. The gels can be customized to provide various electronic functionalities, including electrodes and organic electrochemical transistors (OECT). These inkjet printed cryogel-based devices exhibit high electrical conductivity for embedded conductive polymer traces (up to 350 S/cm), high transconductance for OECTs (in the mS range), and high capacitance in capacitive structures (up to 4.2 mF.g-1). These devices also show high stretchability (up to 330% strain), and self-healing properties. The biocompatible functionalized gel-based electrodes and transistors were successfully implanted in plant tissue. Ionic activity in tomato plants was collected for over two months with minimal scar tissue formation observed over this time, making these cryogel-based electronic devices excellent candidates for continuous, in-situ monitoring of plant and environmental status and health.